The invention is directed to the field of surface mountable chips (SMC's), and more particularly to a series or family of SMC-type band pass filters for frequencies of 30-3000 MHz.
As opposed to components having leads to be "inserted" into holes of a circuit board, SMC's are "onserted" or placed on the circuit board with conductive portions on or near the bottoms of the chips situated for electrical connection by soldering or the like with circuit board tracks. Generally, these are microminiature components which are preferably handled automatically by a pick and place robotic hand or like.
There is an industry need for a series of SMC filters, particularly multisection bandpass filters for the 30-3000 MHz range, which are reliable and easily handled by automated pick and place heads; and it is an object of the invention to meet this need.
It is known to provide multiple thick film layers of conductors and insulators in order to fabricate SMC devices, but such a process doesn't lend itself to assembly of a monolithic substrate with a selected dielectric constant from vendor supplied sheets of material. Examplary of this prior art are U.S. Pat. Nos. 4,342,143; 4,328,531; 4,372,037; and 4,437,140, cross referenced above. "Pinholding", described later, is an additional manufacturing problem in these types of devices.
It is also known to provide SMC filter capacitors of multilayered ceramics, and U.S. Pat. No. 4,516,092 discloses such a capacitor with a discrete inductor attached thereto to complete a filter section. However, the device is particularly directed to a power supply filter and is not concerned with the EMI and RFI problems encountered by the field of the instant invention.
Additionally, it is an object of the invention to provide such a filter wherein plural sheets of suitable dielectric ceramic material are fused together to form a monolithic substrate providing an easily specifiable dielectric constant for the filter capacitors which are formed thereon, and where discrete air core coils provide improved selectivity in the range of 30-3000 MHz.
Further, it is an object of the invention to provide such SMC-type filters in which a ground plane thereof provides one plane of each filter capacitor of the circuit while also substantially enclosing the chip and being attached to a metal cover to provide electromagnetic interference (EMI) and radiofrequency interference (RFI) shielding for the circuit.
Still further, it is an object of the invention that the cover provide a surface by which the component is easily handled by a pick and place tool while also providing physical protection for the fragile air core coils.
These and other objects of the invention will become more apparent from the following detailed disclosure.